The use of wax to provide water repellency in composite board products such as, e.g., particleboard, medium density fiberboard (MDF), and construction boards, etc. is a fast growing application of wax because of growth in the composite board industry. Wax is added to these manufactured wood products to provide adequate water repellency because such cellulose based wood products easily wick in moisture, which can lead to poor dimensional stability of these products. Therefore, wax coating compositions on cellulosic products provide barrier to moisture, water, oil and grease that ultimately protects the mechanical integrity of the material.
Previous studies on optimum wax compositions for water proofing of composite boards and, specifically, particleboards and MDF boards points to n-paraffin content of waxes as the main compositional parameter affecting water repellency. However, the art is rife with conflicting information regarding the effect of wax compositional variables on their waterproofing performance in composite boards.
It is well-known in the art that a narrow molecular weight distribution of paraffin molecules is beneficial for several key properties, including, inter alia, improved water-proofing, hardness, and oil bleed, among others. For example, wax with a wide carbon number distribution is known to be detrimental to the quality of the wax and causes “oil bleed” (Young, F. X. “Practical Applications of Gas Chromatography in Paints and Coatings Industry,” Analysis of Paints and Related Materials: Current Techniques for Solving Coating Problems, American Society for Testing and Materials (ASTM), Philadelphia, 1992, ASTM STP 1119, p 105-124). Oil bleed is the tendency of a wax to have a slick-oily surface and is related to poor wax quality and poor water proofing. Oil bleed in a coating product may provide poor surface characteristics to the coating in terms of poor appearance and lower friction coefficient of the slick coated surface. Similarly, a narrow distribution of carbon lengths and a narrow distillation cut is necessary for production of a high quality wax having sufficient hardness, especially at higher temperatures (Meyer, G. “Interactions between chain length distributions, crystallization behavior and needle penetration of paraffin waxes,” Erdol-Erdgas-Kohle Journal, 2006, 122.Jb, 1, S. 16-18). Finally, the literature has described how increasing molecular weight distribution leads to a decrease in crystal perfection of crystalline materials, which in turn is directly responsible for reduction in barrier properties and water proofing of the material.
For the same reasons, high n-paraffin content is desired in waxes that are used in water proofing applications. High n-paraffin content tends to give a higher percentage of crystalline phase in the material, which in turn is responsible for good barrier properties of the material among other desirable characteristics.
Competing with the ongoing need for paraffin wax materials, including those suitable for use in coating cellulosic materials and composite boards, is the fact that the wax obtained from the Group I refining process, which includes high-quality paraffin waxes, are declining (especially the mid and low carbon numbers), because these wax stocks are more and more frequently consumed for the production of lubricants. Moreover, lower quality paraffin waxes are also recycled and further processed for further lubricant production. In addition, rationalization of Group I refining assets is also reducing the supply of wax. With a reduction in available sources of wax, it has become ever more important to have the flexibility of blending different wax streams without a concomitant deterioration in product properties. However, blending of wax streams with widely different molecular weights or widely different average carbon numbers is well-known to have a negative effect on product properties.
As such, there exists in the art a need for the wax materials that demonstrate properties suitable for industrial use, e.g., coatings for cellulosic materials, candles, writing implements, etc. but that can be produced with lower cost waxes and the flexibility to formulate an optimized wax product for use as a composite board coating with a variety of available wax streams. With the rationalization of Group 1 refining capacity around the world and sharply declining availability of high quality wax streams, a flexibility to use different wax streams to make a suitable product provides a significant advantage.